From gannets to
seagulls, puffins to penguins, all seabirds suffer the same drop in birth rates
when the supply of fish drops to less than a third of maximum capacity. That's
the result from an international study (1) on the relationships between predators
and prey in seven ecosystems around the world, published in the magazine
Science and coordinated by Philippe Cury, an IRD researcher. Based on nearly
450 cumulative years of observation, the research team compared the growth in
fish supplies and the reproductive patterns (2) of 14 species of coastal birds.
These birds mainly feed on sardines, anchovies, herring and prawns, all of
which are victims of over fishing. Below the critical level of one third of the
fish biomass, the birds -- and the stability of the entire ecosystem -- come
under threat.

These studies also
provide a reference level for the sustainable management of fisheries, so as to
safeguard the bird population, which is often imperilled, and so as to maintain
the healthiness of marine environments.

From the Arctic to
Antarctica and from the Atlantic to the Pacific, when the supply of fish is
reduced, seabirds stop reproducing. Previous studies had uncovered the
relationships between the availability of food to birds and their reproductive
rates, but this new international study (1) has just made a monumental
discovery. Coordinated by Philippe Cury, an IRD researcher, and published in
the journal Science, the study identifies the level of a critical supply of
fish below which the stability of the bird population is endangered.

A third's the limit

Gannets, terns,
puffins, seagulls and penguins: taking all the species together, if fish
supplies drop below a third of their maximum size, then the number of baby
birds born drops precipitously. Everywhere in the world. Once the amount of
their prey falls below sufficiency, the seabirds fail to reproduce (2). Yet
above this level, their reproduction rate doesn't increase. Abundance in the
food supply didn't produce the expected result as other factors limit
reproduction, such as the fact that nesting areas fill up quickly.

By demonstrating
such a singular phenomenon, these studies validated empirically -- i.e. from
data rather than from models -- that ecosystems, over the long term, obey
similar laws. Until these studies were carried out, the basic principle of
living ecologies remained theoretical. Now, for the first time, scientists have
achieved a model of predator and prey behaviour based on actual observation in
marine environments.

Almost 450 years of
data

The research team
compared almost 450 years' worth of data from all over the world to see how the
supply of fish correlated with the reproduction of seabirds. To do so, the
scientists concentrated on 14 species of birds in seven ecosystems around the
globe. The species selected feed mainly on sardines, anchovies, herrings and
other small coastline fish that fishermen regularly catch and whose populations
are under pressure. Each of the ecosystems was studied for periods ranging from
15 to 40 years; and the study showed that it generally takes 13 years of data
to form an accurate notion of what the maximum fish supply is in a given
ecosystem.

This is the first
time that so much data on the relationships between predators and prey have
been brought together over such a long period of time. The scientists stressed
cooperation between specialists from the north and the south made it possible
to bring together such a vast quantity of information. Scores of research
specialists have devoted countless years, sometimes their whole career, to
these studies.

Over fishing can
kill ecosystems

This study makes it
plain that over fishing endangers the survival of higher-level predators such
as birds. In fact, they are in direct competition with human fishermen: both
groups consume about 80 million tonnes of fish per year. Small bait which are used
to make meal and oils in fish farming -- such as sardines, anchovies, herring,
smelt and capelin -- make up 30 % of today's catch worldwide. As global demand
rises, these findings make it possible, at last, to achieve a standard against
which to measure the sustainable management of fish, so as to sustain
populations of seabirds, over the long term.

Seabird populations
are one of the best ways to judge the health of marine ecosystems -- which the
European Commission, for instance, wants to be able to monitor -- and are one
of the easiest measurement barometers to use. These bird species are among the
most endangered, owing to the lack of food but also to climate change and the
destruction of coastal habitats where, once again, they are in competition with
humans for space along the water's edge.

In order to
understand the dynamics of ecosystems, it is essential to determine the key
relationships between predators and prey. International authorities today have
few tools by which to gauge and restrict fishing. The limit of one third of the
fish population set forth by this study may not be a hard number in all cases,
but it can certainly serve as a guideline for fishery management policies.

Notes :

(1) These studies
were carried out jointly with scientists from St Andrews and Glasgow
Universities in the United Kingdom, from Ifremer, from the Norwegian Institute
for Nature Research, the Department of Environmental Affairs and the University
of Cape Town in South Africa, the British Antarctic Survey, the University of
Stockholm in Sweden, the University of British Columbia in Canada, the Alaska
Science Center and the Farallon Institute for Advanced Ecosystem Research in
the United States and the Ministry of Fisheries and Marine Resources of
Namibia.

(2)
Reproductive success is the ability of individuals of a species to reproduce,
measured by the number of baby birds that survive.